(1) Field of the Invention
The present invention relates to an improved air extraction apparatus for continuous package making. More particularly, the present invention relates to an improved air extraction apparatus that continuously packages a continuous succession of objects in a continuous length of heat-sealable packaging film. The apparatus extracts air from the packaging film that has been folded in a manner so that margins along opposite longitudinal edges of the film form a seam with two overlapping flaps for heat sealing, wherein just ahead of a heat sealing station, the improved apparatus of the invention extracts air from between the film flaps.
(2) Description of the Related Art
Air suction systems employed with apparatus that continuously package a continuous succession of objects in heat-sealable packaging film are known in the art. Prior art continuous packaging apparatus are typically comprised of several stations that progressively package a series of objects as the objects and a continuous supply of packaging film are conveyed past the stations. The typical apparatus comprise a supply station supplying packaging film in a continuous length to a folding station. At the folding station, the continuous length of packaging film is folded around a continuous succession of objects conveyed past the station. The manner of folding the film produces a continuous, longitudinal tube (usually not cylindrical) of packaging film with the objects enclosed therein. The manner of folding the film also produces a continuous seam along the tube where the opposite lateral edges or margins of the packaging film meet. The seam is formed by overlapping flaps of the film that extend along the longitudinal length of the film tube. After exiting the folding station, the tube and its two overlapping flaps are conveyed to a heat-sealing station that comprises a pair of driven rollers with opposed surfaces for gripping the flaps therebetween. The surfaces of the rollers are heated and seal the overlapping flaps of heat-sealable film together as the overlapping flaps pass between the rollers.
Prior to sealing the packaging film, it is desirable to extract as much air as possible from the interior volume of the packaging, thereby reducing the size of the packaged objects and reducing their shipping costs. For these typical continuous package making apparatus, the present invention is an improvement over the air suction systems of the prior art.
One type of prior art air suction system involves a suction nozzle. In use, the suction nozzle is stationed just ahead of the heat-sealing station. The suction nozzle draws air from the interior of the packaging tube by being positioned between the overlapping flaps of the packaging material as they are conveyed past the nozzle. This mode of operation requires that the nozzle separate the two flaps as they are conveyed past and slide across the opposite sides of the nozzle, with the flaps being rejoined after they have passed the nozzle and air has been extracted from the packaging. Prior art systems of this type are shown by U.S. Pat. Nos. 4,170,863 and 4,663,915.
Another type of prior art air suction system involves a vacuum chamber. The vacuum chamber is defined within a hollow housing positioned underneath or behind a conveyor surface on which the continuous tube of packaging film, with the objects enclosed therein, continuously slides across. The conveyor surface and chamber housing are provided with longitudinal slots that receive a packaging tube's two overlapping flaps as the packaging material is conveyed past the housing of the vacuum chamber. The vacuum chamber communicates with a vacuum pump that creates a vacuum pressure in the chamber housing and draws air from the packaging from between the two flaps during their passage through the chamber housing. Prior art systems of this type are shown by U.S. Pat. No. 5,052,166 and U.K. Patent No. 2,124,995.
Still another type of prior art air suction system involves an eductor pipe connected to a source of vacuum pressure. The eductor pipe is inserted between the two lapped edges of the packaging film at a location still ahead of the heat-sealing station. The eductor pipe extends longitudinally within the confines of the two lapped edges to an open pipe end positioned at a point past the heat-sealing station. Therefore, the eductor pipe extends right through the heat-sealing station, and the heat-sealing station is modified accordingly. Thus this type of an air suction system works on a different principle from the others in that air is siphoned out of the tube of packaging material at a location along the tube that is past the heat-sealing station rather than ahead of it. A prior art system of this type is shown by U.S. Pat. No. 4,272,944.
There are several disadvantages associated with the prior art systems. The type involving a nozzle is often unable to provide a desirable degree of vacuum. This results from numerous leaks which permit the reentry of air into the tube. The leaks are difficult to avoid because the overlapping flaps of packaging material must be separated in order for them to slide over the opposite sides of the nozzle. There are open voids between the flaps both before and after they pass around the nozzle and, in consequence, air persistently leaks between the passing flaps and stationary nozzle. This system is also disadvantaged in that the flaps will often be displaced from their positions extending around the nozzle as the packaging material is conveyed past the nozzle, requiring the system to be closed down until the flaps are repositioned.
The type of prior art air suction system involving the vacuum chamber is likewise unable to provide a desirable degree of vacuum. The leaks are present here because of the configuration of the longitudinal slot, and particularly because of the configuration of the entry and exit ends of the slot. The slot ends are open to permit the sliding entry and exiting of the continuously passing flaps of packaging material. The slots are often configured to be wide enough to avoid the imposition of any frictional engagement drag on the flaps being conveyed through the slot. Yet this also means that there are gaps between the flaps and the slot side walls that permit air from outside the packaging to leak into the slot. The result is a low operating efficiency and a less than desirable degree of vacuum.
The type of prior art air suction system involving an eductor pipe is chiefly deficient in requiring a modified, non-typical apparatus for continuous package making. These types of prior art air extraction systems have specialized constructions that are not readily retrofit to existing packaging conveying systems.